1. Field of the Invention
The present invention relates to an armature of a rotary electric machine and to a method of manufacturing the armature. The invention is to provide an armature which has conductors of an increased density in the slots of the armature, and which features increased reliability in electric insulation.
2. Description of the Prior Art
To increase the density of conductors in the slots of the armature makes it possible to decrease the slot areas, provided the amount of the conductors remains the same in the slots, and hence to reduce the flux density in the core.
Accordingly, iron losses can be reduced and exciting current can be reduced, to enhance performance of the rotary electric machine. When the performance is maintained the same, the size of the armature core can be reduced and the weight can be reduced to save resources.
For this purpose, a method has already been proposed in U.S. Pat. No. 3,348,183 to Ralph D. Hodges and Francisco C. Avila of producing a coil which helps enhance the conductor density in the slots, by pressing portions of a coil side to change the cross-sectional shape of the conductor from a circular shape into a polygonal shape.
According to this method, a coil side is placed in a ring-like molded member having a hardness greater than that of the coil conductor, and is subjected to the pressing, so that the cross-sectional shape of the conductor is changed from a circular shape into a non-circular shape.
With this method, however, the wires located in the outer periphery and in the inner periphery of the coil side are also deformed from the circular shape into a non-circular shape. Therefore, when a great pressure is exerted, the insulation film applied onto the surface of the electric wire is destroyed and the dielectric strength is greatly deteriorated. In particular, the dielectric strength decreases greatly with a copper wire having a high hardness compared with an aluminum wire. Therefore, the armature in a rotary electric machine loses reliability in insulation. If a reduced pressure is exerted to decrease the amount of deformation thereby to maintain the reliability in insulation, the object will not then be accomplished.
Another method has also been proposed in U.S. Pat. No. 3,515,919 to Jack A. Houtman and Holland Mich.
According to this method, a coil side of a main winding is placed in a slot, and the conductors are plastically deformed. Then, a starting field winding is inserted in space that is formed near the opening of the slot as a result of plastic deformation.
With this method, however, it is not possible to increase the ratio of the sectional area of a coil side to the sectional area of a slot (hereinafter referred to as space factor) in a stator in which one coil side is placed in one slot. This is because the slot is formed in a semi-enclosed shape in which the opening portion is covered by the end of teeth that are located on both sides of the slot. With the semi-enclosed slot, a pressing board for pressing the coil side must have a width greater than the width of the opening of the slot, must be inserted in the slot from the axial direction of the stator core, and must be moved toward the bottom of the slot.
Therefore, if the pressing board is removed from the slot after the coil side has been pressed, the opening portion of the slot simply turns out to be idle space which does not help increase the space factor.
Japanese Patent Publication No. 33786/1983 has been proposed by Teruhisa Motojima and Izumi Shimizu. According to this proposed method, one electric wire is placed in a slot and is pressed by the pressing board, and then another electric wire is placed on the previously pressed electric wire and is pressed by the pressing board. This operation is carried out repetitively to increase the space factor in the slot.
According to this method, however, the electric wire which is initially placed in the bottom of the slot is subjected to the pressing the greatest number of times, and the insulation film thereof is most likely to be destroyed. In small electric machines, furthermore, the stator coil must be wound several tens to several hundreds of times, requiring tremendously long periods of time for the pressing operation.